1. Field of the Invention
The present invention relates to a tandem-type pump having an auxiliary pump, and more particularly to a tandem-type pump having an auxiliary pump being provided with an auxiliary shaft which is installed in an extension housing disposed adjacent to and driven by a driving shaft of a tandem-type and wobble plate-type piston pump for construction equipment.
2. Description of the Prior Art
Generally, construction equipment is provided with a tandem-type and wobble plate-type piston pump. In the piston pump, two main pumps are connected with each other in a coaxial relationship and are driven by a single driving shaft. The driving shaft of the piston pump is connected with an auxiliary shaft. The auxiliary shaft is driven by the driving shaft. The auxiliary shaft operates an auxiliary pump being used as an auxiliary hydraulic power unit or as a pilot hydraulic power unit for the construction equipment by receiving a driving force from the driving shaft.
FIG. 1 is a schematic sectional view of an auxiliary pump according to the prior art.
FIG. 2 is a sectional view taken along a line A--A of FIG. 1.
Referring to FIGS. 1 and 2, a middle block 3 is disposed in the middle of a housing 1. A connector 6 is installed in the middle block 3. The connector 6 connects a left portion of a driving shaft 4 with a right portion of the driving shaft 4, which are coaxially aligned and are separated from each other by the middle block 3.
The left portion and the right portion of the driving shaft 4 are simultaneously driven by the connector 6. Thereby, wobble plate-type piston pumps, which are positioned at both sides of the driving shaft 4, begin to operate.
Meanwhile, teeth are formed at an outer periphery of the connector 6. The teeth of the connector 6 are engaged with a first idle gear 9. The first idle gear 9 is engaged with a second idle gear 10 in sequence. The second idle gear 10 is engaged with teeth formed at an outer periphery of an auxiliary shaft 8 for driving an auxiliary pump. Since a large number of gears are engaged with each other in sequence as described above, the auxiliary shaft 8 receives a driving force from the connector 6, which is located in the middle of the main pump, in order to connect the left portion with the right portion of the driving shaft 4. In other words, since an outer diameter of the teeth formed at the outer periphery of the connector 6 is limited by the available space of the middle block 3, the driving force provided by the connector 6 is transmitted to the auxiliary shaft 8 through a large number of gears.
In the tandem-type pump having the auxiliary pump as described above, it is necessary to have two to three idle gears and a plurality of supporting bearings 11 for supporting the idle gears. Accordingly, the number of components and the number of stages for transmitting the driving force are increased. As a result, heavy noise and severe vibration can be generated during engagement of the gears for transmitting the driving force, and thereby the loss of the driving force is highly increased.
Further, in the tandem-type pump according to the prior art, an additional auxiliary pump block 13 is mounted to the middle block 3 in order to transmit the torque of the driving shaft 4 to the auxiliary shaft 8. In the same manner as the middle block 3, the auxiliary pump block 13 is provided with a plurality of idle gears and a large number of bearings for supporting the idle gears. Accordingly, the total weight of the tandem-type pump is highly increased. As a result, the center of gravity of the tandem-type pump offset from a mounting flange (not shown). The mounting flange couples the main pump to the construction equipment. The center of gravity offset thereby produces a moment of inertia in the tandem-type pump. Consequently, the driving stability of the increased tandem-type pump deteriorates due to the vibration occurring during operation of the tandem-type pump.